Field of Invention
The present invention relates generally to building ventilation systems, and more particularly to an air-to-air regenerative heat recovery ventilator (HRV) employing a rotary damper assembly suitable for HRV and other applications.
Background Art
Ventilation systems have become an indispensable part of a building's construction since laws, regulations and building codes have required increased energy-saving measures, such as insulation, weather stripping, and other means for sealing the interior of a building from the outside climate. Sealed buildings require a regular supply of fresh air to maintain a safe and comfortable environment in the interior space. Building ventilation systems provide this supply of fresh air. However, when the air in the interior space is replaced on a frequent basis, the heating, air conditioning, humidifying, and dehumidifying systems of the building are called into operation on a frequent basis to heat, cool or otherwise condition the fresh air, which results in an increase in energy consumption. In order to mitigate this increase in energy consumption, a heat recovery ventilator (HRV) can be employed between the outside of the building and the building's ventilation system. HRVs include one or more heat exchangers for recovering heat during the ventilation process. The building's ventilation system creates a supply airstream by drawing fresh air in from outside, and creates an exhaust airstream by exhausting stale air out to the outside. Usually, an “air-to-air” HRV is employed, using heat exchangers to transfer heat between the supply and exhaust airstreams. It is “air-to-air” because it transfers heat between two airstreams. In the winter months, the exhaust airstream is the warmer and more humid of the two airstreams, and thus the heat exchangers of the HRV transfer heat (sensible and latent) from the exhaust airstream to the supply airstream. In the summer months, the supply airstream is the warmer and more humid of the airstreams, and thus the heat exchangers transfer heat (sensible and latent) from the supply airstream to the exhaust airstream.
One particular type of air-to-air HRV is a “fixed bed” regenerative HRV. It is “fixed bed” because it uses fixed (stationary) heat exchangers, and it is “regenerative” because each heat exchanger temporarily stores heat and then later releases it (i.e., regenerates the heat). This type of HRV has at least two heat exchangers and a mechanism for routing and rerouting the exhaust and supply airstreams through the heat exchangers in an alternating fashion. For example, a warm exhaust airstream is initially made to flow through a first heat exchanger (“HE”) and transfer its heat to the first HE (“hot period”), and a cool supply airstream is initially made to flow through a second HE and absorb heat energy previously stored in the second HE (“cold period”). After a certain time interval, the airstreams are switched, so the cool supply airstream flows through the first HE and absorbs the heat stored there during the previous period, and the warm exhaust airstream flows through the second HE and transfers its heat to the second HE, which was cooled during the previous period. A HE is said to have completed one cycle of operation after undergoing both a hot and cold period. By using at least two HEs in such alternating fashion, essentially continuous heat transfer operation is achieved between the airstreams. Each HE contains a storage mass or matrix suitable for storing and releasing sensible and latent heat energy from the airstreams. Examples of such fixed bed, air-to-air regenerative HRVs are disclosed in U.S. Pat. No. 6,450,244 and U.S. Patent App. Pub. No. 2011/0076934.
In some air-to-air regenerative HRVs, the mechanism for switching the airstreams includes a damper that reciprocates between first and second air-deflecting positions. The damper is a generally flat rectangular member that simultaneously deflects both exhaust and supply airstreams. The damper causes the exhaust and supply airstreams to be routed to first and second HEs, respectively, when it is in the first air-deflecting position, and routed to the second and first HEs, respectively, when in the second air-deflecting position. An example of an HRV with such a damper is shown in FIGS. 1, 4a & 4b of U.S. Pat. No. 6,450,244. This type of HRV with reciprocal damper has proven to be an effective system. However, the damper requires compression sealing around all of its four edges when it is in one of the air-deflecting positions. Sealing is required to isolate one airstream from another. In this type of HRV, the damper plays a critical role in effecting the seal along these edges. The damper compresses the seals (against metal stops) along the damper's edges to create an air-tight or air-resistant seal. The fact that the damper serves as part of the sealing mechanism and its compression against another part of the seal is required, imposes certain enhanced structural and force requirements on the damper. The damper must be rigid and strong enough to be compressed against the seals with adequate force. Movement of the damper between the air-deflecting positions requires more than a positioning force; it further requires a compression force to effectuate the seal.
A better understanding of the above can be had by considering FIGS. 1 and 2 herein. FIG. 1 shows the construction of a prior art damper assembly 10. Assembly 10 includes a damper 12 having a structural steel tube frame 14 covered on each broad side with a sheet-metal skin 16a, 16b. Due to the weight of damper 12, three sturdy bearings 18a, 18b, 18c are employed to support the damper for reciprocating rotational movement about an axis 20. Damper 12 is mounted in a housing 22 (FIG. 2). Bearing 18a is mounted on or in a side wall or floor of housing 22 (mounting not shown). A lower drive shaft 24 rotatably engages bearing 18a and is attached to a first end of frame 14 (along axis 20). An upper drive shaft 26 extends through bearing 18b at a first end and through bearing 18c at a second end. The first end of shaft 26 is attached to a second, opposing end of frame 14 (along axis 20). Drive shaft 26 extends to the exterior of housing 22 and includes a crank arm 28 fixed to the shaft. Crank arm 28 is connected to a piston arm of a pneumatic cylinder actuator 30. Actuator 30 is mounted on a steel frame 32. Steel frame 32 is situated between damper 12 and bearing 18b. Bearing 18b is mounted on steel frame 32. Actuator 30 is enclosed by an actuator cage 34 on frame 32. Bearing 18c is mounted on top of actuator cage 34. Actuator 30 is connected, via a compressed air line (not shown), to an air compressor 36. Compressor 36 provides the pneumatic force to move the arm of actuator 30 between extended and retracted positions, causing arm 28 to move damper 12 between air-deflecting positions. A damper reversing valve 37 is also included to reverse the action of actuator 30. A utility housing 38 may be provided to house frame 32, bearing 18b, drive shaft 26, crank arm 28, actuator 30, cage 34, bearing 18c, reversing valve 37, compressor 36, and perhaps electronic controls (not shown).
FIG. 2 is a schematic illustration of the prior art damper seal arrangement. FIG. 2 shows damper 12 in cross-section (along a line perpendicular to axis 20). Mounted on a housing wall 40 is an arrangement of compression-type damper (or side) seals 42a, 42b, 42c and 42d, each of which is affixed to an elongated metal stop 43. A matching arrangement of damper seals and stops are mounted on an opposing wall of housing 22 (out of the paper). Depending on the orientation of damper 12, wall 40 could be a side wall, floor or ceiling of housing 22. Running between wall 40 and the opposing wall of housing 22 are compression-type transverse (or end) seals 44a, 44b, 44c and 44d, also backed by metal stops, respectively. As understood from FIG. 2, all four edges of damper 12 are sealed when damper 12 is forced against seals 42a-42d and seals 44a-44d in either air-deflecting position.
FIGS. 1 and 2 make clear that the prior art damper is a significant steel frame structure with the attendant weight. The weight is substantial enough to require three sturdy bearings, two drive shafts, and a crank arm. It also requires a pneumatic drive system to move it between operative positions and to compress it against an intricate arrangement of seals. The pneumatic cylinder produces such force that it requires a strong steel support frame to hold it in position. And, of course, the drive system requires a supply of compressed air or a compressor. Thus, the damper, damper seals, and pneumatic drive system make up an elaborate damper assembly, which comes with a cost in materials, assembly, and maintenance over the life of the HRV. Also, the pneumatically driven damper creates noise. It will make a thumping sound when it is compressed against the seals. The volume of the thump can be reduced by reducing the speed of the damper, but proper damper operation requires the damper to move as fast as possible. Thus, a tradeoff exists between optimum damper speed and the volume of noise of the damper. The compressor and pneumatic cylinder actuator also emit noise during their operation. A need plainly exists for a quieter, simpler and more cost effective damper assembly in a fixed bed, air-to-air regenerative HRV.
Fixed bed, air-to-air regenerative HRVs have been made without a pneumatic drive system. For example, U.S. Patent App. Pub. No. 2011/0076934 discloses the use of electric motors to operate dampers in an HRV; however, four dampers and at least two electric motors are required. Another example is in U.S. Pat. No. 6,257,317, which discloses the use of an electric motor to drive a rotating “air switch.” The air switch rotates in 90 degree steps, over 360 degrees, in a process that alternately directs airstreams between HEs. The air switch has openings in its side walls to produce axially directed flows of the airstreams between the air switch and the HEs. Other examples of similar rotating air switches or valves in HRVs are shown in the following patents: U.S. Pat. No. 2,701,129; U.S. Pat. No. 3,047,272; U.S. Pat. No. 4,688,626: and U.S. Pat. No. 7,441,586.